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<div class="titlepage"><div><div><h3 class="title">
<a name="math_toolkit.fp_facets.rationale"></a><a class="link" href="rationale.html" title="Design Rationale">Design Rationale</a>
</h3></div></div></div>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            The flags are implemented as a const data member of the facet. Facets
            are reference counted, and locales can share facets. Therefore changing
            the flags of a facet would have effects that are hard to predict. An
            alternative design would be to implement the flags using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">xalloc</span></code> and <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios_base</span><span class="special">::</span><span class="identifier">iword</span></code>.
            Then one could safely modify the flags, and one could define manipulators
            that do so. However, for that to work with dynamically linked libraries,
            a <code class="computeroutput"><span class="special">.</span><span class="identifier">cpp</span></code>
            file would have to be added to the library. It was judged be more desirable
            to have a header-only library, than to have mutable flags and manipulators.
          </li>
<li class="listitem">
            The facet <code class="computeroutput"><span class="identifier">nonfinite_num_put</span></code>
            throws an exception when the <code class="computeroutput"><span class="identifier">trap_infinity</span></code>
            or <code class="computeroutput"><span class="identifier">trap_nan</span></code> flag is set
            and an attempt is made to format infinity or NaN. It would be better
            if the facet set the <code class="computeroutput"><span class="identifier">fail</span> <span class="identifier">bit</span></code> of the stream. However, facets
            derived from <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">num_put</span></code> do not have access to the stream
            state.
          </li>
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      Gautam Sewani, Benjamin Sobotta, Nicholas Thompson, Thijs van den Berg, Daryle
      Walker and Xiaogang Zhang<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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